Motor vehicles of the truck or trailer type are generally backed up to a loading dock for loading and unloading the truck or trailer at the loading dock. Loading docks may also be provided with manually or hydraulically operated load levelers which include a lip to bridge the gap between the motor vehicle and the top of the loading dock. The load levelers are controllable to position a loading lip member partially into the motor vehicle at an elevational level to allow relatively smooth travel between the loading dock and the inside of the motor vehicle. The use of load levelers also permits the use of material handling devices, such as fork lift trucks, or the like, for the loading and unloading operations. It is known that a motor vehicle parked adjacent the loading dock may be inadvertently or unexpectedly moved away from the loading dock during the loading and unloading operations resulting in damage to equipment and injury to personnel. Conventionally, the undesired movement is prevented by the use of wheel chocks secured under the tires of the motor vehicle for restraining the movement of the motor vehicle. Failure to utilize the wheel chocks by the motor vehicle operator and problems experienced therewith has resulted in the development of a restraining device for mechanically engaging and disengaging the bumper of a truck or trailer. For this purpose, the Interstate Commerce Commission, ICC, specifies a type of bumper or bar that must be secured to the rear of the truck or trailer to prevent low profile vehicles from running completely under the vehicle in rear end collisions. The ICC bars or bumpers have been found useful with the aforementioned mechanical restraining devices. The bumper or bar permits a mechanical hook or the like to be positioned into engagement with the bumper for restraining the movement of the motor vehicle when the two are interlocked. These prior art restraining devices are normally secured to the side wall of the loading dock and are adapted to be moved into a restraining position with the bumper. One such prior art restraining device is disclosed in U.S. Pat. No. 4,208,161. The patented restraining device is secured to a loading dock in a fixed position and is manually operative to interlock with an ICC bumper. The device is completely mechanical and is moved under the ICC bumper to a restraining position therewith. Other commercially available devices are movable along the side wall of the loading dock to move underneath the ICC bumper for releasably interlocking a hook-like member with the bumper. Signalling devices are also in use in combination with the motor vehicle restraining devices for signalling the condition of the restraining device, in storage or use, to permit the motor vehicle operator and/or personnel loading or unloading the motor vehicle to be aware of the actual condition of the restraining device from their work stations or from the motor vehicle by viewing the signalling device or display device. The operation of such restraining devices has also been integrated with the use of hydraulically operated load levelers for the loading dock. All presently known restraining devices protrude forwardly of the loading dock in the path of the travel of the motor vehicles to and from the loading dock.